Quasi‐6‐Day Wave Effects on the Equatorial Ionization Anomaly Over a Solar Cycle

The quasi‐6‐day wave (Q6DW) has recently been recognized as an important source of ionospheric variability. This study shows how the response of the equatorial ionosphere to the Q6DW changes over a solar cycle. Global maps of total electron content (TEC) from Global Positioning System data are used to quantify Q6DW effects on the equatorial ionization anomaly during 2004–2017. The results are compared with the Q6DW amplitude in the lower thermosphere as derived from the geopotential height measurements by the Aura satellite. A nearly one‐to‐one correspondence is found between Q6DW activities in the ionosphere and lower thermosphere, indicating robust vertical coupling. The absolute amplitude of the Q6DW in low‐latitude TEC varies with the solar activity index F 10.7 and can reach 8 TEC unit (=10 16 el/m 2 ) near the crests of the equatorial ionization anomaly during solar maximum. On the other hand, the relative amplitude is unaffected by solar activity, with its annual maximum value being ∼10% for both solar minimum and solar maximum. These results establish the persistent influence of the Q6DW on the equatorial ionosphere under different solar activity conditions.